That's pretty close to my definition as well, though I add FATAL as well, but mostly for extreme cases of "there's no way the system can function" type of error

That's pretty close to my definition as well, though I add FATAL as well, but mostly for extreme cases of "there's no way the system can function" type of errors, such as missing/invalid configuration or similar. My philosophy is that INFO is the default runtime configuration. At smallish scales (< 1B requests/month) I've seen this approach work very well, especially when the Eng team is on board with high-quality log messaging. It was an investment to get to that state at my last startup, but the massive improvement to QoL for Eng and Ops teams was totally worth it.